The mechanical properties and the durability of natural building stones are influenced to a large extent by inherent inhomogeneities. One of such inhomogeneities is a stylolite, particularly when it occuts in carbonate-rich rocks. Stylolites are irregular surfaces in which small tooth-like projections on one side of the surface fit into cavities of like shape on the other side. Many stylolitic carbonate rocks are generally dense and sound, and may perform excellently when used as facing stones or tiles. However, there are other types that are of infe¡ior quality due to the type of materials filling the stylolites. To the naked eye, such rocks may appear dense, homogenous and impermeable, but on a microscale, the stylolites may contain porous, permeable and water-sensitive materials, such as smectites that can adversely affect the durability of such rocks when exposed to the atmosphere. Experience shows that the use of an integrated method, consisting of t¡aditional physical, non-destructive and durability tests, in combination with optical microscopy and X-ray diffraction analysis, often offers an invaluable means of evaluating the quality of such materials. In this paper, the use of such an integrated method to assess damage due stylolites in two separate natural stones is presented and discussed.